1. Field of the Invention
The present invention relates to a light-emitting unit. Particularly it relates to a light-emitting unit constituted by a combination of a light-emitting device and a fluorescent material.
The present application is based on Japanese Patent Application No. 2000-258090, which is incorporated herein by reference.
2. Description of the Related Art
There has been developed a light-emitting unit in which apart of light emitted from a light-emitting device is subjected to wavelength conversion by a fluorescent material and the part of light which has been subjected to wavelength conversion is mixed with the other part of the light which has not been subjected to wavelength conversion to thereby emit light with an emission light color different from that of the light emitted from the light-emitting device.
For example, a light-emitting unit using a group III nitride compound semiconductor light-emitting device as a light-emitting device for emitting blue light and using an yttrium-aluminum-garnet fluorescent material (YAG) activated with cerium (Ce) as a fluorescent material has been put on the market. In such a light-emitting unit, for example, a cup portion of a lead frame in which a light-emitting device is mounted is filled with a light-transmissible material containing a dispersed fluorescent material (YAG) to thereby form a fluorescent layer in the light-emitting direction of the light-emitting device. In such a configuration, when the light emitted from the light-emitting device passes through the fluorescent layer, a part of the light is radiated after the part of light is absorbed by the fluorescent material (YAG) or the wavelength of the part of light is converted by the fluorescent material. The other part of light is radiated after transmitted through the fluorescent layer without being absorbed by the fluorescent material. As a result, the two kinds of light are mixed with each other to thereby obtain emission of white light.
An object of the present invention is to provide a novel-configuration light-emitting unit constituted by a combination of a light-emitting device and a fluorescent material. Another object of the present invention is to provide a light-emitting unit high in light-emitting efficiency. A further object of the present invention is to solve the following problems in the background-art light-emitting unit.
According to the present inventors"" examination, the color of the emitted light obtained by the aforementioned light-emitting unit is bluish or greenish white. Development of a light-emitting unit for obtaining higher-quality white light has been demanded. That is, development of a light-emitting unit for emitting white light containing red, green and blue components with good balance has been demanded.
The aforementioned light-emitting unit is relatively expensive because the fluorescent material (YAG) used in the light-emitting unit contains rare metal. As a result, the cost of production of the light-emitting unit increases.
It is further difficult to adjust color mixing of the light from the light-emitting device and the light from the fluorescent material, so that it is difficult to stably produce a light-emitting unit with a constant emission color. That is, to obtain a constant emission color, a predetermined quantity of light needs to be converted in wavelength by the fluorescent material. Hence, in the aforementioned background-art configuration, the thickness of the fluorescent layer provided in the light-emitting direction of the light-emitting device needs to be kept constant. It is however difficult to control the thickness of the fluorescent layer accurately because the fluorescent layer is formed, for example, by dripping a fluorescent material-containing light-transmissible material into the cup portion after the light-emitting device is mounted on the lead frame.
The inventors of the present invention have made eager examination to achieve at least one of the foregoing objects. As a result, the following configuration has been conceived. That is, according to the present invention, there is provided a light-emitting unit which comprises:
a light-emitting device for emitting light with a wavelength range of from 360 nm to 550 nm; and
a fluorescent material made of Caxe2x80x94Alxe2x80x94Sixe2x80x94Oxe2x80x94N oxynitride activated with Eu2+;
wherein a part of light emitted from the light-emitting device is emitted outward after it is subjected to wavelength conversion by the fluorescent material.
According to the aforementioned configuration, there can be provided a light-emitting unit constituted by a novel combination of a light-emitting device with a specific emission peak wavelength and a fluorescent material made of Caxe2x80x94Alxe2x80x94Sixe2x80x94Oxe2x80x94N oxynitride activated with Eu2+. In the aforementioned configuration, the fluorescent material is excited by light with a wavelength range of from 360 nm to 550 nm and efficiently emits light with a wavelength longer than that of the excitation light. Hence, the light-emitting unit configured as described above has high emission efficiency. Moreover, the fluorescent material in the aforementioned configuration has a preform composed of Ca, Al, Si, O and N. Hence, it can be said that the fluorescent material can be produced from a general and inexpensive material compared with the fluorescent material (YAG) used in the background art. Hence, a light-emitting unit low in the cost of production can be provided.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.